DATA DESCRIPTION: These data
consist of the monthly PDSI over global land areas computed using osberved
or model monthly surface air temperature (from Jones and Moberg 2003 and
updates) and precipitation (see above papers), plus other surface forcing data for the
sc_PDSI_pm case.

***Update on Nov. 2, 2015: The 1850-2014 scPDSIpm data file was revised using following steps:
a) a narrower raonge of -10 to +10 was imposed, b) the time series at each grid box was scaled
to have the same standard deviation as over the central U.S. during the calibration period from
1950-1979, and c) small gaps were infilled using bilinear interpolation using nearby values.
These new steps improve the spatial homogeneity although temporal inhomogeneity may still exist
for a small number of grid boxes in northern Africa and other regions. Users should check the data
series before applicaitons, especially for periods before 1950.
***Update on Feb. 24, 2016: The 1850-2014 scPDSIpm data file was revised with slight changes from
the previous version of Nov.2, 2015. Users are advised to update their applications with this updated
version.

Temporal (left, black) and spatial (right) patterns of the two leading
EOFs of the monthly PDSI (normalized by its standard deviation prior to
the EOF analysis). Red (blue) areas are dry (wet) for a positive
temporal coefficient. Also shown in the left-lower panel (red) is the
Darwin mean sea level pressure shifted to the right by six months to
obtain the maximum correlation (r=0.62). Variations on < 2 year time
scales were filtered out in the left panels. The percentage variance
explained is shown on the top of the left panels. (From Dai et al.
2004)